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and March 1976 when it was at the X-ray low state. Fifty-eight early-type stars which lie within 10° of HDE 245770 were also observed by the ANS, and these stars were used to derive a localized extinction curve. From the depth of the 2200 Á interstellar absorption feature observed in the ANS flux distribution of HDE 245770 and the shape of the localized extinction curve, an E(B -V) = 0.72 is derived for HDE 245770. This system was observed during its X-ray flare-up (October 1980) and quiescent (November 1981) states by the IUE. The fine error sensor on board the IUE detected an increase in the optical brightness of HDE 245770 during the X-ray outburst. This greatly strengthens the identification of HDE 245770 as the optical counterpart of A0535-I-26. There was no significant change in the absorption-line profiles during the X-ray high and low periods indicating that there was no significant increase in the stellar wind density when the X-ray flare-up occurred. The UV continuum level increased by < 5% when it was near peak X-ray luminosity. The UV spectrum of HDE 245770 indicates that it is a B0 V or a B0 III star with its dereddened continuum slope slightly in favor of being a giant. A0620-00 was observed by the ANS in March 1976 when its X-ray and optical brightness were rapidly decaying. Twenty-five early-type stars were used to establish a localized extinction curve and an E(B -V) = 0.35 was derived by using the ANS data obtained by Wu et al. when the system was near X-ray and optical maximum. The dereddened UV and optical continuum shape for the 1976 March period can be described by a combination of 60% T = 18,000 K blackbody and 40% F v = constant spectra.

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